1. Field of the Invention
The present invention relates to a fuel vaporizer for internal combustion engines for promoting vaporization of fuel films or particles attached to the wall of an intake passage by heating such fuel films or particles.
2. Description of the Prior Art
Fuel supplied to internal combustion engines tends to form films or large particles or droplets, instead of being finely vaporized, and become attached to the inner wall of an intake passage when the engine is started or is driven at low speeds. When such fuel films or droplets are present in the engine, the exhaust gas emitted therefrom contains an increased amount of harmful pollutants such as carbon monoxide and hydrocarbons, and the distribution of an air-fuel mixture among engine cylinders is poor. It is known that by heating the fuel films or large fuel droplets for evaporation, the exhaust gas is cleaned, and the air-fuel mixture gets distributed evenly among the engine cylinders, resulting in smooth engine operation.
There has been proposed a fuel vaporizer comprising a sheath heater composed of an electrical resistor or a thermistor having a positive temperature coefficient of resistance (PTC thermistor) for heating and evaporating fuel films or droplets flowing down or attached to the intake passage wall at the time of starting the engine under cold conditions. Although the proposed fuel vaporizer is effective to evaporate fuel droplets or films, it consumes a large amount of electrical power and takes a long period of time before it is heated to a desired temperature since the heater needs to be internally or bodily heated. Use of the known fuel vaporizer oftentimes requires an increase in the capacity of the generator and storage battery provided on the car for energizing the fuel vaporizer.